What are "kidney cysts"? Should I be worried? How do you treat them?

Cysts, or abnormal pockets of fluid filled sacs, are a common finding on imaging studies like ultrasounds that are done on the kidney. I often see concerned patients in consultation about this finding. The question in that situation is...should you be worried if you discovered that you have cyst/s in your kidney?


HOW COMMON ARE KIDNEY CYSTS?

Cysts in the kidney are a pretty common occurrence. They tend to get more prevalent in the older age groups. For instance, 11.5% of individuals aged 50-70, and 22.1% of all individuals aged over 70 yrs will have at least one cyst in the kidney. However, the challenge is to identify whether it is a benign age related finding or something as serious as cancer (which can present as cysts). Cysts often will have no symptoms, and will usually be discovered incidentally as part of imaging of the kidneys for unrelated reasons.

WHAT CAUSES KIDNEY CYSTS?

Kidney cysts are often a part of the aging process of the kidney. However, they can be a manifestation of other pathological and more serious diseases of the kidney. Some of these disease are inherited or have a genetic link (like polycystic kidney disease, medullary cystic disease, etc), or can be acquired (benign simple cysts, acquired cysts in patients with advanced kidney disease, etc). 


Kidney Cysts: To Worry or Not to Worry?
Image courtesy of Dream Designs/FreeDigitalPhotos.net



WHAT FEATURES OF A KIDNEY CYST SHOULD MAKE YOU CONCERNED?

You might need assessment from a nephrologist to answer this. In my opinion, a diagnosis of a "kidney cyst" is a "radiological finding"; it is not the complete diagnosis. The first question that needs to be answered is whether the cyst is "simple" (with thin walls and no solid tissue), versus complex (thick walls, septations or partitions inside, solid tissue, etc). Usually, the way to characterize this is by doing a CT scan. Based on the appearance on the CT scan, the cyst will often be given a so-called "Bosniak classification". Cysts are classified from category 1(simple) through 4 (most complex) on this scale. Grade 4 cysts are almost always cancerous, and the treatment would require resecting part of the kidney, or even the entire kidney. 

Does that mean that a diagnosis of "simple cyst" is necessarily a benign harmless diagnosis? Not always. This is because other characteristics like the total number of simple cysts, their location, the size, and whether the kidney size is enlarged, are important factors. For instance, multiple cysts in each kidney where the kidney size in not enlarged could well be a case of multiple benign simple cysts (requiring no specific treatment other than the nephrologist keeping an eye on them). However, if the kidney architecture is distorted and the kidneys are bigger than normal, it could be a case of polycystic kidney disease (that will often progress to kidney failure requiring dialysis or transplantation). 


WHAT IS THE TREATMENT FOR KIDNEY CYSTS?

Treatment would depend on the cause and the type of kidney cysts. Complex cysts that have a high grade Bosniak classification will need to be removed with part of- or the entire affected kidney, given the concern about cancer. As mentioned above, simple cysts would usually not require treatment other than a nephrologist keeping an eye on your kidney numbers and cyst apperance. However, sometimes even simple kidney cysts could require treatment should they become symptomatic. These symptoms could be:

  • Pain: If the cyst is painful to the point where painkillers are not helpful, they can be aspirated, "unroofed" (to open them up), or decorticated.
  • Hypertension: When a cyst presses on the tissue of the kidney, it can sometimes cause the kidney to produce chemicals that raise your blood pressure. This can usually be managed medically by a specific class of medications called ACE inhibitors or ARBs.
  • Infections: Should a cyst fluid become infected, it will require treatment with specific antibiotics that need to be able to penetrate through the cyst wall. Examples of such antibiotics include fluoroquinolones (eg. ciprofloxacin).


Needless to say, the algorithm on how to approach kidney cysts can often get complicated, and requires then input of a kidney doctor.

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